RECON, a geotechnical company, owns a state-of-the art Casagrande jet grouting drill rig capable of a 60-foot long stroke. The hydraulic rig includes an automated system to control the grouting process based on the operator´s programmed parameters and an automated grout batch plant.

Jet grouting can be used regardless of soil type, permeability, grain size distribution, etc. In theory, it is possible to stabilize most soils, from soft clays and silts to sands and gravel. Although it is possible to inject any type of binder, in practice water / cement mixtures are normally used. Where impermeabilization of the soil is required, water / cement / bentonite mixes are typically utilized.

A subsurface slurry wall can be formed by sequentially jet grouting adjoining columns of soil. An advantage of jet grouting over other slurry wall techniques is it can be used to stabilize a wide range of soils ranging from gravel to heavy clays. A secondary advantage is that large diameter columns or panels can be created from relatively small diameter boreholes. Therefore, slurry walls can be constructed beneath buildings with limited disruption of the structure itself by using jet grouting techniques.

Jet Grouting Case Studies

PORT OF TEXAS CITY
Texas City, Texas

The alignment of a sheetpile bulkhead, under construction at the Port of Texas City to allow dredging in order to increase the draft around the wharf, crossed beneath an operational access way/pipe rack. The original bulkhead design provided for construction of a slurry trench cutoff wall beneath the access way to bridge the gap bewteen the installed sheetpile sections. However, in view of potential constructibility issues given the limited headroom, difficult access, and depth of excavation, Remedial Construction Services, L.P. (RECON) proposed an innovative, single-fluid jet grouting alternate.

Jet Grouting is a replacement/mixing technology that uses a high-pressure "jet" of grout to erode and mix the in situ soil, creating a blended mass of grout and soil with high strength and low permeability. Jet grouting equipment is designed for low headroom and limited access situations, ensuring that closure could be readily and safely accomplished within the confines of the work area without any possibility of equipment contact with the access way and associated piping. Furthermore, jet grouting would reduce project costs.

Jet Grout Cutoff Design and Construction
The 53-foot long cutoff wall was to be installed to a depth of 45 feet through a soil profile consisting of surficial clay overlaying medium grained sand, with stiff, high PI clay encountered at 45 feet. Prior to production work, test columns were installed to verify the design parameters of a maximum permeability of 1x10-7 cm/sec and a minimum unconfined compressive strength (UCS) of 350 psi.

The jet grout columns were installed using RECON´s state-of-the-art equipment, including an automated grout batch plant, high-pressure pump, a hydraulic drill equipped with an extended mast capable of a 60-foot long stroke, and an automated system to control the grouting process based on the operator´s programmed parameters. At either side of the access way, interconnecting jet grout columns of varying length were installed at angles ranging from vertical to within 15 degrees of horizontal, creating two, fan-shaped wall segments that intersected to form a continuous wall. Production quality control measures included verification of the grouting parameters established by the test columns, verification of column alignment, and retrieval and testing of grouted soil samples for permeability and UCS. Forty-eight, 36-inch diameter columns were installed to complete the cutoff.

Additional Work
RECON also installed a total fluids hydrocarbon groundwater recovery system approximately 30 feet landside of a 200-foot stretch of bulkhead in order to extract diesel. This involved connecting 23 well vault recovery skimmer pumps into an automated product storage tank. Contaminated soils encountered were disposed as Class I non-hazardous waste. Five recovery trenches were also installed at various strategic areas close to the channel water edge to collect any potential offsite product flow.

SIMS BAYOU
Houston, Texas

Sims Bayou is a major stormwater conveyance feature that comes under the auspices of the U.S. Army Corps of Engineers (USACE). When a deep failure plane–caused by the presence of low-strength soils combined with a seasonal upward hydraulic gradient–developed along a stretch of the bayou´s 20-foot high embankment, the USACE selected the single-fluid jet grouting technique to stabilize the slope.

Jet grouting is a replacement mixing technology that uses a high-pressure jet of grout to erode and mix the soils in situ, creating a blended soil/grout matrix with improved engineering properties.

Jet Grouting Program
The intent of the jet-grouting program was to intercept the active failure plane and prevent further soil movement into the bayou. Deleterious material was excavated and the area was backfilled to construct a stable working platform. Jet grouting was accomplished using Remedial Construction Services, L.P. (RECON´s) state-of-the-art equipment, including an automated grout batch plant, high-pressure pump, and hydraulic drill equipped with a single-fluid jet grout drill string. RECON installed 120,30-inch diameter jet grout columns to a depth of 32 feet, creating a stabilized zone of soil approximately 100 feet long and 10 feet wide. The project was successfully completed within the 240-day schedule.

Quality Control and Quality Assurance
Prior to production work, six test columns were installed within the area of the permanent system. After being allowed to cure, all six columns were excavated and visually inspected to verify that the required column diameter could be achieved in the highly plastic Gulf Coast clays. One unconfined compressive strength (UCS) test was performed for every ten production columns to ensure that the specified minimum UCS of 250 psi in 28 days had been achieved.

Site Restoration
In addition to the jet-grouting program, RECON performed the following items of work at the site:

• Installation of silt barriers to protect Sims Bayou during construction,
• Installation of a cellular concrete mattress from the base of the jet-grouted section to below the water line to prevent erosion of the slope into the bayou.
• Installation of relief wells and drainage structures, and
• Restoration of the slope to its pre-failure condition, including turfing and tree planting.